This invention relates to oscillatory tooth and needle gear transmitting devices of the kind in which a set of separately movable intermediate parts, the oscillatory teeth, are used to accomplish motion and power transmission, which are generally used for speed reduction transmission but can also be utilized for speed increasing or differential gear transmission.
A transmitting device using separately movable intermediate parts to accomplish mechanical transmission is essentially a kind of planetary gear transmission with small tooth number difference. It differs from ordinary planet gear transmission mainly in the fact that a set of separately movable intermediate parts are used to replace the planet gears which are in planetary movement (planar movement). Since two "higher pairs" are formed between the contacts of intermediate parts and the driver or follower parts, there exist four curves of "tooth profiles." Under the condition of constant speed conjugation between moving pairs, if any three of the curves are prescribed, the fourth can be determined using the method of envelope curve, four meshing designs being thus obtained. In early oscillatory tooth transmitting devices, such as DT1204466, SU214257 and the "sliding tooth speed reducer" manufactured by British Sanderson Brothers and Newbould Limited, the profile curve of driver part (an eccentric circle) and the curves of the two ends of movable intermediate parts (the oscillatory teeth) are prescribed, and the tooth profile curve of follower parts is determined by using the method of envelope curve. Generally this curve is special, very difficult to manufacture and undesirable in transmitting characteristics. The application and development of such designed transmitting devices are therefore limited. In U.S.S.R. Pat. No. SU1036979 is introduced a mechanical transmitting device in which the follower part is structured as a needle gear, i.e., a ring gear assembled by cylindrical pins. The driver part is still an eccentric circle and the oscillatory tooth has a plane bottom and a triangular head. Since it has no special tooth profile, this kind of transmitting device is much easier to manufacture, the primary obstacle for it to be popularized being eliminated. During each reciprocating cycle of the oscillatory teeth in the transmitting device introduced in U.S.S.R. Pat. No. SU1036979, the follower part is driven by the meshing force between the tooth profiles of oscillatory teeth and needle gear in the working stroke, but the oscillatory teeth are pulled back by elastic return ring (reference No. 5 in Fig. of SU1036979) during the backward stroke rather than by the meshing force between tooth profiles. Furthermore, it is obvious from the figure that the thickness of the plate-structured oscillatory teeth is evidently smaller than the space between two needle teeth. Should there not be an elastic return ring to pull back the oscillatory teeth, they would be inserted into the space between needle teeth, unable to return back and self-locked, making the transmitting device unable to work. In the prior arts aforementioned, most of them have complicated tooth profiles, and all of them have to use elastic return rings. It has been proven by both theory and practical application that there is a greater circumferential friction between oscillatory teeth and the elastic return ring, and the latter causes some interference among oscillatory teeth. This not only lowers the transmission efficiency, but also increases the noise level. In addition, the oscillatory teeth in U.S.S.R. Pat. No. SU1036979 have triangular heads which, driven by the eccentric circle, result in an approximate mesh with the needle gear. If geometric parameters are improperly chosen, they will cause unsteady angular speed and unequal load. An elastic ring (reference No. 5 in Fig. of SU1036979) is thus needed in said patent to function as a compensatory element. When meshing in the tip area, there will be a larger pressure angle unfavorable to tooth strength for the oscillatory tooth. Moreover, the oscillatory tooth in U.S.S.R. Pat. No. SU1036979 is plate-structured, its width (measured along the axis of speed reducer) being 2-3 times larger than its thickness. This kind of structure is unfavorable to the strength and rigidity of the oscillatory tooth wheel, more difficult in machining and inconvenient to have a symmetric twinrow arrangement for balancing the load and increasing the transmitting capacity. The unequal load along the width of the head of oscillatory tooth is yet another problem difficult to be solved.